How much does 8% over a 36-year career grow?

Question

You invest steadily at 8\% a year for a 36-year working life. Solve in your head. Roughly how many times does the money multiply by retirement? Aim: under 15 seconds.

Accepted Answer

Doubling time: \frac{72}{8} = 9 	ext{ years.} Number of doublings over the career: \frac{36}{9} = 4 \;\Rightarrow\; 2^{4} = 16	imes. Check: 1.08^{36} \approx 16.0, essentially exact. Takeaway. A career-length horizon at market-like returns is worth roughly four doublings, a 16	imes multiple. This is the single most persuasive argument for starting to invest early: the last doubling alone adds as much as everything before it combined.

How much does 8% over a 36-year career grow?

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